Traditional electric hair trimmers have a serious problem that they are easily stuck with secretions or accumulated with dirt when trimming hairs; even though the secretion or dirt is rinsed in time, residues are inevitable due to the fine and compact structure of the hair trimmer; after a long time of accumulation, not only sanitation problem appears and disgusting smell comes out, but also cutters are highly likely to be blocked and thus lose the hair cutting function, especially in cold or dry weathers; or, due to low battery or insufficient driving force, an electric machine cannot start a moveable blade stuck to a fixed blade, causing the moveable blade unable to make a reciprocating motion relative to the fixed blade to realize cutting. This problem troubles designers for a long time and must be overcome.